Speed control device

ABSTRACT

A speed control device working with hydraulic fluid makes use of a displacement type pump. The pressure head delivered by the pump is used directly as control pressure actuating a servo-motor. The pressure head is dependent upon the pump speed which, in turn, is a function of the speed to be controlled. The regulating range of the pressure head of the pump is increased by a differential pressure controller, making use of a nozzle member, cooperating with a diaphragm and a throttle plate.

United States Patent Kalb 1 Dec. 2, 1975 [54] SPEED CONTROL DEVICE2.111.964 3/1938 Crane 60/468 2.456.431 12/1948 Price 60/329 [75] KalbNuremberg Germany 3.392.633 7/1968 Kokuly 60/468 X [73] Assignee:AEG-Kanis Turbinenfabrik GmbH,

Numberg Germany Primary E.\'aminer-Edgar W. Geoghegain [22] Filed: June13, 1974 [211 Appl. No.: 479,181 [57] ABSTRACT [30] Foreign ApplicationPriority Data A skpeed corfitroidelvice workting with hyqdgnulic fluidma '65 use 0 a isp acement ype pump. e pressure June 1973 Gummy 2331282head delivered by the pump is used directly as control pressureactuating a servo-motor. The pressure head is 60/325 i g ighg dependentupon the pump speed which. in turn, is a Fie'ld 459 468 function of thespeed to be controlled. The regulating range of the pressure head of thepump is increased by a differential pressure controller, making use of anoz- References Cited zle member, cooperating with a diaphragm and athrottle late. UNITED STATES PATENTS p 2.005 731 6/1935 Ernst ct a].60/329 6 Claims, 4 Drawing Figures SPEED CONTROL DEVICE BACKGROUND OFTHE INVENTION The invention relates to a speed control device workingwith hydraulic fluid and comprising a displacement type pump whichserves as signal transmitter of the device. It has been attempted tomake use of such a dis placement type pump for speed control devices.Difficulties have been encountered however, because the pressure head ofsuch a pump increases only slightly when the rate of output flow of thepump increases in a linear proportion according to the speed.

Therefore, the pressure head of the pump is ineffective for a use to actdirectly upon a final control element in order to control a mass flow ofan engine. In addition, the volumetric slip of a displacement type pumpand alterations in the viscosity of a pressure oil may distort thecontrol signal.

SUMMARY OF THE INVENTION It is an object of the invention to provide aspeed control system making use of a displacement type pump.

It is another object of the invention to improve the sensitivity ofresponse of the pressure controller of such a control system.

It is a further object of the invention to increase the working capacityof the servo-motor by increasing the output pressure range of thepressure controller.

Finally, it is an object of the invention to provide an integratedcontrol system which is integrated together with the servomotor into onehousing.

The foregoing objects are achieved in accordance with the presentinvention by providing a speed control device working with hydraulicfluid and including a displacement type pump and comprising anadjustable orifice which is the inlet of a valve chamber thatcommunicates by that orifice with the high pressure side of the pump.The control device comprises further a differential pressure controllercomprising a valve forming a first outlet of the valve chamber. Thevalve comprises a nozzle member and a throttle plate carried by adiaphragm and cooperates with the mouth of the nozzle member which opensinto the valve chamber. Further the diaphragm is charged from within thevalve chamber by a spring force, which is directed against the throttleplate. The diaphragm and the throttle plate forms one wall of the valvechamber and separates it from a second chamber. This second chambercommunicates on the one hand with the high pressure side of the pump bya viscosity dependent throttle and on the other hand with the mainoutlet of the valve chamber by an adjustable throttling device. Thecontrol pressure to actuate the piston of a servo-motor is delivered bythe main outlet of the valve chamber.

By using a differential pressure controller provided with a diaphragmthe sensitivity of response of the pressure controller is very high.

The main advantage achieved by the invention is that no pump of theprecision type is required although the exactness of speed controlachieved is excellent, whereas the influence of alterations in theviscosity of the hydraulic fluid used is very weak. This is so becausethe viscosity alterations are compensated for by the viscosity dependentthrottle and the adjustable throttle following each other. Theintermediate pressure be- 2 tween them actuates the diaphragm and itsthrottle plate from the other side of the nozzle member.

In a preferred embodiment of the invention the speed -control device andthe servo-motor are integrated in one and the same housing so that theeffectiveness of the servo-motor is improved, because the controlpressure can directly actuate the piston of the servo-motor.

In this embodiment preferably a negative feedback is achieved when thespring, charging the ball of the second valve, is supported by thepiston of the servomotor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of thecontrol device according to the invention.

FIG. 2 shows the curves of different pressures of the hydraulic fluid inthe control device.

FIG. 3 is a longitudinal sectional view of the control ler andservo-motor housing.

FIG. 4 is a sectional view of an example of an adjustable orifice usedin the arrangement according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning now to the figures, theinvention will be explained in detail.

In FIG. 1 the circuit diagram shows the control device including thedisplacement type pump 50, the differential pressure controller D, anegative feedback valve RV, the servo-motor SV and a relief pressure andsafety valve UV.

The main duct 101 leading to the servo-motor charging it with thecontrol pressure p receives pressure oil from the ducts 103, 105 and106. An adjustable orifice 19 is installed in the duct 106 for settingthe rated value of speed, while a throttle 22 and an adjustable throttle20 are installed in the duct 105. The duct 104 leads from the reliefpressure valve UV to the outlet and return duct 102.

The pressure in the main duct 101 is specified as p,, the dischargepressure of the pump 50 as p, and the pressure in the return duct 102 asp,,. The pressure oil reservoir 108 is indicated by a dash-dot line.

The pressures indicated as p, and p are intermediate pressures, theirsignificance will follow from the description of FIG. 3.

The speed X of the machine to be controlled may be adjusted by aconventional valve (not shown) controlling, for example, the main powerduct for fuel in the case of an internal-combustion machine or turbine,or the main steam supply of a steam turbine. The adjusting of the valveis effected by the stem rod 41 of the piston 2 belonging to theservo-motor SV (see FIGS. 1 and 3).

The movements of the piston 2 depend in a proportional relation on thedeviations of the speed of the machine to be controlled, since thedisplacement type pump is coupled to a rotating member of the machine aswill be explained now turning to FIG. 3. FIG. 3 shows the pressurecontrol device and the servo-motor integrated in one housing. Theservo-motor comprises a piston 2, biased by a spring 4, and a piston rod41. The latter can be coupled e.g. with a stem of a valve which governsthe flow of elastic fluid of a turbine, and it may be likewise coupledwith a valve device adjusting the fuel flow of an internal-combustionmachine or a gas turbine. The hydraulic fluid arrives from the highpressure side of the displacement type pump 50, which 3 may be a gearpump, e.g. of the-straight spur or the helical type, to the inlet of avalve chamber 17. The inlet is formed by an adjustable orifice 19 whichserves as'the setpoint adjuster for the desired speed of the engine tobe controlled.

Furthermore the pressure in the valve chamber 17 depends on the pressurep, in a second chamber separated from the valve chamber 17 by adiaphragm l2 and a throttling plate 14, carried by the diaphragm.

The hydraulic fluid arrives in the second chamber 10 through a throttle22, which is formed by a narrow channel or bore of a certain length sothat its throttling effect depends on the viscosity of the hydraulicfluid, since as it is well known, the pressure loss depends on theReynolds number. In this manner the influence of the viscosity iscompensated for.

The throttling plate 14 is further biased by a spring 18. It followsfrom the above that the fluid flow escaping from the valve chamber 17through the mouth 16 and the bore 13 of the nozzle member decreases bythe same ratio as the pressure p, in the second chamber 10 increases. Inthis manner there is provided a constant difference between the pressurep, in the second chamber 10 and the pressure p, in the valve chamber 17.Consequently there is effected a nearly constant fluid flow throughorifice 19. Because the delivery of the pump is, by this means,restricted to be nearly constant too, the pressure head of the pump 50increases at the same ratio as its shaft revolutions increase with therotating engine member with which the pump 50 is coupled. The controlpressure p which passes from the main outlet 40 of the valve chamber 17through a channel 31 to the piston chamber 25 where it actuates thepiston 2, is increased accordingly.

The movement of the piston 2 may then be transmitted to a furtherregulating device, e.g. a final control valve as described above.

With decreasing speed the effect is contrary. For regulating theproportional band of the control device, a second throttle is providedwhich is adjustable. There is additionally generated a negative feedbackby the spring 8 which is supported by the piston 2 and transmits springforces to the valve ball 6 which are proportional to the movements ofthe piston 2.

Accordingly there is, in the bore 13 of the nozzle member 15 a pressureis generated which, acting on the throttle plate, causes a certainquantity of hydraulic fluid to escape from the valve chamber 17 throughthe bore 13, to an extent proportional to the magnitude of the pressurein the bore 13.

This quantity of fluid flows off through the outlet 27. A safety valve,formed by a ball 29 biased by a spring 30 opens a passageway to theoutlet 27, whereby the pump 50 is protected against overload.

Turning now to FIG. 2 it will be explained now how the volumetric slipof the displacement type pump 50 is compensated for. This compensationis effected by the differential pressure controller which generates apressure p so that the course of the curve p, is steeper than that ofthe curve p,, the pressure head of the pump 50. As a result, there isobtained a differential pressure p p, which diminishes from Ap to Approportional to increasing speed, i.e. revolutions of the pump, and ac-4 cordingly, proportional to increasing movement Y of the final controlelement.

Accordingly there is a diminished flow of hydraulic fluid throughorifice 19 at the same rate as the slip of the pump 50 increases; inthis way the slip is compensated for.

The adjustable orifice 19 shown in detail in FIG. 4 consists of athreaded screw having an incision 61 at its hollow tip 62 which extendsinto a bore 60. The flow through the bore depends on the position of theincision 61 relative to the bore which can be adjusted by the knurl 65.A ring-seal 63 is provided between two shoulders of the screw.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations and it is intended to cover in the appended claims all suchmodifications which fall within the scope of the invention.

I claim:

1. A speed control device working with hydraulic fluid and including adisplacement type pump, comprising an adjustable orifice being the inletof a valve chamber that communicates through said orifice with the highpressure side of said pump, and a differential pressure controllerincluding a valve forming a first outlet of said valve chamber, saidvalve including a nozzle member and a throttle plate carried by adiaphragm and cooperating with the mouth of said nozzle member openinginto said valve chamber, the said diaphragm being charged from withinthe valve chamber by a spring force, the said diaphragm and throttleplate being one wall of said valve chamber separating it from anadditional chamber, the additional chamber communicating with the highpressure side of said displacement type pump and with a second, mainoutlet of said valve chamber through a throttling device, the said mainoutlet of said valve chamber delivering the control pressure actuating apiston of a servo-motor.

2. Speed control device according to claim 1, wherein said additionalchamber communicates with the high pressure side of said displacementtype pump through a viscosity dependent throttling device.

3. Speed control device according to claim 1, wherein said nozzle has anozzle bore, the outlet of which opposite the nozzle mouth is governedby a second valve.

4. Speed control device according to claim 3, wherein said second valveis a ball biased by a spring.

5. Speed control device according to claim 4, wherein said controldevice and said servo-motor are arranged in one housing, saidservo-motor including a piston and a piston rod movable in a pistonchamber of said housing, a first part of said piston chamber being thepressure side where the control pressure is actuating the piston, asecond part of said piston chamber situated on the other side of saidpiston being provided with an outlet for the flow-off of pressure oil,the said nozzle bore communicating with said second part of said pistonchamber through said second valve, said spring biasing the valve ballbeing supported by said piston.

6. Speed control device according to claim 5,.

wherein said piston is biased by a second spring pro-

1. A speed control device working with hydraulic fluid and including adisplacement type pump, comprising an adjustable orifice being the inletof a valve chamber that communicates through said orifice with the hIghpressure side of said pump, and a differential pressure controllerincluding a valve forming a first outlet of said valve chamber, saidvalve including a nozzle member and a throttle plate carried by adiaphragm and cooperating with the mouth of said nozzle member openinginto said valve chamber, the said diaphragm being charged from withinthe valve chamber by a spring force, the said diaphragm and throttleplate being one wall of said valve chamber separating it from anadditional chamber, the additional chamber communicating with the highpressure side of said displacement type pump and with a second, mainoutlet of said valve chamber through a throttling device, the said mainoutlet of said valve chamber delivering the control pressure actuating apiston of a servomotor.
 2. Speed control device according to claim 1,wherein said additional chamber communicates with the high pressure sideof said displacement type pump through a viscosity - dependentthrottling device.
 3. Speed control device according to claim 1, whereinsaid nozzle has a nozzle bore, the outlet of which opposite the nozzlemouth is governed by a second valve.
 4. Speed control device accordingto claim 3, wherein said second valve is a ball biased by a spring. 5.Speed control device according to claim 4, wherein said control deviceand said servo-motor are arranged in one housing, said servo-motorincluding a piston and a piston rod movable in a piston chamber of saidhousing, a first part of said piston chamber being the pressure sidewhere the control pressure is actuating the piston, a second part ofsaid piston chamber situated on the other side of said piston beingprovided with an outlet for the flow-off of pressure oil, the saidnozzle bore communicating with said second part of said piston chamberthrough said second valve, said spring biasing the valve ball beingsupported by said piston.
 6. Speed control device according to claim 5,wherein said piston is biased by a second spring provided in said secondpart of said piston chamber.